1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus having the same. More specifically, the present invention relates to a zoom lens suitable to an image pickup apparatus using a solid-state image sensor, such as a video camera, a digital still camera, a broadcast camera, or a monitoring camera, or to an image pickup apparatus using silver-halide film.
2. Description of the Related Art
In recent years, an image pickup apparatus using a solid-state image sensor, such as a video camera, a digital still camera, a broadcast camera, or a monitoring camera, has multiple functions. Furthermore, the size of such an image pickup apparatus is small.
In addition, it is desired by the market that a photographic optical system used in an image pickup apparatus has a short total lens length, a compact (small) size, and a high zoom ratio (high variable magnification ratio), and that a zoom lens has a high resolution.
A positive-lead type zoom lens in which a lens unit having a positive refractive power is located on the object side is widely used to respond to the desire. For example, a zoom lens is widely used that includes a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a rear lens unit including one or more lens units, which is located following the third lens unit.
In such a zoom lens, the second lens unit having a negative refractive power implements a main variable magnification by moving towards the image side during zooming from the wide-angle end to the telephoto end. Moreover, in such a zoom lens, the lens configuration of the third lens unit is significant in achieving high optical performance for the entire zoom range.
In a zoom lens discussed in U.S. Pat. No. 5,963,378, a third lens unit includes one or more positive lenses and negative lenses. Furthermore, an aperture stop is located just in front of the third lens unit.
In zoomlenses discussed in U.S. Pat. No. 6,606,202, Japanese Patent Application Laid-Open No. 08-94931, U.S. Pat. No. 7,199,942, and U.S. Patent Application Publication No. US 2006/0146417 A1, a third lens unit includes three lenses and an aperture stop is located between the lenses of the third lens unit to achieve high optical performance for the entire zooms area.
Furthermore, in a zoom lens discussed in U.S. Patent Application Publication No. 2006/0146417 A1, a third lens unit can be moved in a direction having a component perpendicular (orthogonal) to an optical axis to correct an image shake in a captured image occurring when the zoom lens is vibrated.
In a zoom lens discussed in U.S. Pat. No. 7,199,940, a part of the lenses constituting a third lens unit can be moved in a direction perpendicular to an optical axis to correct an image shake occurring when the zoom lens is vibrated.
In recent years, it is strongly desired by the market that a zoom lens used in an image pickup apparatus has a high zoom ratio and has a lens system whose total size is small.
Generally, in a zoom lens, if the refractive power of each lens unit is intensified, then the moving amount for moving each lens unit for obtaining a predetermined zoom ratio can be reduced. Accordingly, if each lens unit has a high refractive power, a high zoom ratio can be achieved and the total lens length can be shortened.
However, an assembling accuracy for each lens unit may be degraded when the refractive power of each lens unit is merely intensified. For example, in the above-described conventional zoom lens, if the optical axis of each lens in the third lens unit becomes relatively offset during assembling of the third lens unit, which may greatly affect the optical performance of the zoom lens, an image performance may degrade.
Accordingly, in the above-described positive-lead type zoom lens, it is highly important to appropriately set the lens configuration of a third lens unit to achieve a small-size zoom lens having high optical performance.
Furthermore, with respect to a digital camera or a video camera, it is desired that a high optical performance can be achieved even if the camera is vibrated.